THE SMITHSONIAN INSTITUTION. 



407 



Sulphur instead of phosphorus gave no action until it was fused hj 

 means of a hot metal ring ; the galvanometer was then instantly 

 deflected. 



In another experiment both tubes of the battery were charged with 

 nitrogen, but one was provided with })hosphorus, the other with 

 iodine. After closing, a decided current appeared which lasted for 

 months. 



The nitrogen did not change in volume, but the liquid became 

 gradually colored. Here the vapor of iodine acted like oxygen ; the 

 vapor of phosphorus like hydrogen. 



§ 46. The pole changer. — It is well knov/n that if two homogeneous 

 plates, say of platinum, be immersed in dilute acid, the poles being 

 connected even with only a single voltaic element, the galvanic pohiri- 

 zation which they undergo if connected after the interruption of the 

 primary current, is sufficiently strong to cause a current in the oppo- 

 site direction. For example, let a, in Fig. 33, be a vol- 

 tameter, b a galvanic element, sending its current through 

 the latter ; the current being interrupted, connect the 

 terminal v^^ires of a multiplier c witli the two plates, and 

 this will indicate a current of polarization which, however, 

 will soon cease. 



In this manner a whole series of plates can be polarized, 

 and thus we obtain Bitters secondary jnle, for charging 

 which a primitive battery ot many pairs of plates is always 

 used. The electro-motive force, which sets in motion the 

 current of the secondary battery, is evidently less than 

 that of the primary charging battery. 



Poggendorff has invented a contrivance for charging, 

 with a simple voltaic battery a secondary battery of any number of 

 plates, and thus obtains a current of far greater electro-motive force 

 than that of the charging battery itself. (Pog. Ann. LX, 5G8.) 



The process is as follows : Suppose we have a series of pairs of pla- 

 tinum i)lates, in cells, filled with dilute sulphuric acid, as shown in 

 Fis- 34. Fig. 34. Plates 1 and 2 are in the first 



cell, 3 and 4 in the second, &c. Now, if 

 plates 1, 3. 5, and 7 be connected with the 

 positive pole of the simple battery, and the 

 plates 2, 4, 6, and 8 with the negative 

 pole, the plates denoted by the odd num- 

 bers will be negatively polarized^ (since 

 oxygen escapes at their surfaces.) and the 

 plates denoted by even numbers Avill be 

 positively polarized, (by hydrogen.) 



After this connexion has existed only a 

 very short time, it must be suddenly broken, 

 the charged plates connected according to 

 the principle of the battery^ and the cir- 

 cuit closed by a voltameter ; this will now 

 be traversed by a current of much greater tension than the primitive 



